title: Competition for spectral irradiance between epilimnetic optically active dissolved and suspended matter and phytoplankton in the metalimnion. Consequences for limnology and chemistry.
abstract: In deep lakes, water column stratification isolates the surface water from the deeper bottom layers, creating a three dimensional differentiation of the chemical, physical, biological and optical characteristics of the waters. Chromophoric dissolved organic matter (CDOM) and total suspended solids (TSS) play an important role in the attenuation of ultraviolet and photosynthetically active radiation. In the present analysis of spectral irradiance, we show that the wavelength composition of the metalimnetic visible irradiance was influenced by epilimnetic spatial distribution of CDOM. We found a low occurrence of blue-green photons in the metalimnion where epilimnetic concentrations of CDOM are high. In this field study, the spatial variation of the spectral irradiance in the metalimnion correlates with the observed metalimnetic concentrations of chlorophyll a as well as chlorophyll a : chlorophyll b/c ratios. Dissolved oxygen, pH, and nutrients trends suggest that chlorophyll a concentrations were representative of the phytoplankton biomass and primary production. Thus, metalimnetic changes of spectral irradiance may have a direct impact on primary production and an indirect effect on the spatial trends of pH, dissolved oxygen, and inorganic nutrients in the metalimnion.
authors.affiliation: Consorzio Interuniversitario per lo sviluppo dei sistemi a Grande Interfase, CSGI, Dipartimento Farmaco Chimico Tecnologico, Università di Siena, Siena, Italia. bracchini@unisi.it
authors.forename: Luca
authors.initials: L
authors.lastname: Bracchini
authors.forename: Arduino Massimo
authors.initials: AM
authors.lastname: Dattilo
authors.forename: Margherita
authors.initials: M
authors.lastname: Falcucci
authors.forename: Vincent
authors.initials: V
authors.lastname: Hull
authors.forename: Antonio
authors.initials: A
authors.lastname: Tognazzi
authors.forename: Claudio
authors.initials: C
authors.lastname: Rossi
authors.forename: Steven Arthur
authors.initials: SA
authors.lastname: Loiselle
mesh_terms: D018533:Biomass; D002734:Chlorophyll / Q000737:chemistry; D000077194:Chlorophyll A; D006863:Hydrogen-Ion Concentration; D010100:Oxygen / Q000737:chemistry; D010839:Phytoplankton / Q000737:chemistry*; D012621:Seasons; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D002734:Chlorophyll; C064041:chlorophyll c; C037184:chlorophyll b; D010100:Oxygen; D000077194:Chlorophyll A